For the mechanical seal used as the shaft seal to a centrifugal pump or so, the inside of the stuffing box of which the mechanical seal is provided will temporarily be negative pressure upon starting, hence this causes the condition having no liquid on the sliding face of the mechanical seal, and may cause a burning or breaking of the sliding face.
In order to solve such problems, conventionally the double mechanical seal (it may be simply referred as the double seal) is used in some cases. In the double mechanical seal, by flowing the quenching liquid between the two seals, it prevents the sliding face from drying. Also, the double seal is frequently used in case the liquid is not to leak out to the inner device side, or in case the liquid of the inner device side becomes crystallized by drying or so.
For example, as shown in the below patent article 1, the double mechanical seal combining the bellows is known. However, such conventional double mechanical seal comprises the rotary ring per each mechanical seal, and the rotary rings are arranged at two positions along the axis direction of the rotary shaft, therefore the constitution of the device in the axis direction was long, and it did not satisfy the demand of making it more compact.
Also, for the double mechanical seal with the conventional bellows, the stationary ring has a constitution of shrink-fitting to the retainer (the adaptor), thus in case the inner side pressure of the bellows is high, there is a risk that the sealed fluid leaking between the stationary ring and the retainer. Also, for the conventional double mechanical seal with the bellows, as the stationary ring has the constitution of shrink-fitting to the retainer (the adaptor), in case the pressure difference between the outside and the inside of the stationary ring is reversed, the adhesive force working toward the seal face between the stationary ring and the rotary ring significantly changes. Therefore, in case the pressure difference between the inside and the outside of the bellows is reversed, it is necessary to change the design of the double mechanical seal with the bellows (such as spring force of the bellows or so), and it is necessary to prepare the different double mechanical seal depending on the pressure difference atmosphere.